Well, Terry, seems you have stumped the house with this one. I have always had flatirons grilled, and I think most people are used to them that way. The beauty of them is that they are (or have been) cheaper than many cuts, and you still get a good mix of flavor and tenderness with them. Smoking probably won't ruin them, just be careful about keeping them to the rare-med side, and maybe giving them a blast on the grill for finish appearance. Good luck!